<!doctype html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>Document</title>
</head>
<body>
	<div>
		
	</div>
	<canvas id="canvas" width="600" height="600"></canvas>
	<script>
	var canvas = document.getElementById('canvas');
	var context = canvas.getContext('2d');

	context.lineJoin = 'round';
	context.lineWidth = 30;
	context.font = '24px Microsoft Yahei'
	context.fillText('click anywhere to erase',175,200)
	context.strokeStyle = 'goldenrod'
	context.fillStyle = 'rgba(0,0,255,0.5)'
	context.strokeRect(75,100,200,200)
	context.fillRect(325,100,200,200)
	context.canvas.onmousedown = function(e){
		context.clearRect(0,0,canvas.width,canvas.height)
	}
	</script>
</body>
</html>